Storage tube with secondary emissive storage grid



D. W. ROE

March 29, 1966 STORAGE TUBE. WITH SECONDARY EMISSIVE STORAGE GRID Filed Oct. 8, 1965 SGS wh um; NEQ

gpm/AMIWT af- United States Patent O 3,243,644 STORAGE TUBE WITH SECONDARY EMISSIVE STORAGE GRID Donald W. Roe, Lancaster, Pa., assigner to Radio Corporation of America, a corporation of Delaware Filed Oct. 8, 1963, Ser. No. 314,688 12 Claims. (Cl. 315-12) The present invention relates to display storage tubes of the multimode type and particularly to a storage tube having an improved storage grid.

A multimode display storage tube is one in which stored and non-stored information may be displayed simultaneously. For example, the stored information may comprise a non-moving background, and the non-stored information may be a moving display superposed on the non-moving background.

One type of multimode display storage tube includes several guns. One group of guns is associated with the storage feature of the tube. This group comprises two guns. One of these guns is a writing gun that produces a beam of electrons that is scanned across a storage grid and suitably modulated in intensity to provide a desired electrical charge pattern on the grid. The storage grid is disposed between this gun and a phosphor screen. The other electron gun of the one group of guns comprises a reading gun for providing a flood of electrons directed towards the storage grid. The passage of the flood electrons through the grid is modulated by the charge pattern on the grid, so that some of the electrons pass through the grid and strike the screen, and other electrons are turned back by the grid. The ele-ctrons that strike the phosphor screen produce a display thereon. Since the flood electrons do not disturb the charge pattern on the storage grid, the display produced by electrons from the flood gun remains on the screen so long as the flood gun supplies electrons.

A single gun is employed in connection with the nonstorage function of the multimode type of display storage tube under consideration. This gun may be used to produce one or more of several effects including a moving or other non-stored display on the phosphor screen. For a moving display the beam of electrons produced by this gun is intensity modulated by a suitable signal and scanned across the storage grid. The electrons from this gun that pass through the grid provide a moving display on the screen. Since the electrons from this gun that pass through the grid produce only immediate or transient effects on the screen, it may be considered to be a gun which produces a beam which is non-storing at the storage grid, but which illuminates the phosphor screen, and thus functions substantially in a manner similar to that of a gun of a cathode-ray tube of the kinescope type.

One of the problems associated with multimode display storage tubes concerns the properties of the dielectric material employed as a storage medium on the storage grid of such tubes. This material should not only possess the required resistivity for the normal storage functions of the tube, but also should have a characteristic that assures preservation of stored information on the storage grid during the formation of the non-stored display. This characteristic should be such that the electron dislodged from the storage grid by secondary emission when struck by the non-storing beam are replaced by an equal number of electrons supplied to the storage grid.

While this balance can be preserved theoretically by a material having a secondary emission characteristic at the second crossover of the emission curve, such material is difficult to provide on a practical scale.

A more satisfactory way to provide the desired balance between the electrons lost by the storage target by second- Patented Mar. 29, 1966 ICC ary emission, and electrons supplied to the target, is to employ a dielectric target material having such a secondary emission characteristic that operation is between the first and second Crossovers of the emission curve, coupled with a certain bombardment-induced conductivity.

One grid coating material heretofore suggested for this purpose is a particular type of zinc sulfide applied as a layer on the gun side of the metallic grid base. This type is cubic zinc sulfide. This type of zinc sulde possesses a minimum resistivity for useful service as a storage medium and responds in conductivity to bombardment by electrons to counteract the loss of electrons therefrom by secondary emission.

However, it was believed that special processing of zinc sulfide was required for its conversion into the cubic form. Such processing involves particular temperatures and environment, and is time consuming, thereby adding to the cost of the tube.

Furthermore, while it was believed that zinc sulfide in the cubic form had higher resistivity than zinc sulfide in other forms such as hexagonal or amorphous, it was thought desirable for best results to employ a dielectric material for a multimode storage tube that exhibits an even higher resistivity than cubic zinc sulfide.

Accordingly it is an object of the invention to provide an improved multimode display storage tube.

A further object is to facilitate the manufacture of a storage grid for a multimode display storage tube.

Another object is to provide an improved storage grid for a multimode display storage tube.

These objects are realized in a multimode display storage tube having a storage grid including a metal mesh having on the gun side thereof a dielectric in the form of an outer layer of zinc sulde in any form, and an intermediate layer of cadmium sulfide. The cadmium sulfide forms a blocking interface with the material of the mesh that exhibits a rectifying characteristic. This rectifying characteristic inhibits electron tiow through the interface from the mesh to the dielectric, when the mesh is at a more negative potential than the dielectric.

The two layers in combination with the blocking or rectifying interface, have an appreciably higher resistivity than cubic zinc sulfide alone, for advantageous service in a multimode display storage tube.

Further features and advantages of the invention will become apparent as the present description continues.

Referring to the drawing for an example of a tube embodying the invention:

FIG. l is a partly schematic view in longitudinal crosssection of a direct View display storage tube in which the present invention is used;

FIG. 2 is an enlarged cut-away perspective View of the storage grid of the tube shown in FIG. l;

FIG. 3 is an enlarged fragmentary view in cross section of the storage grid shown in FIG. 2; and

FIG. 4 shows a graph illustrating certain characteristic curves of the tube depicted in FIG. l.

GENERAL The direct view display storage tube 10 shown in FIG. l includes an envelope 11 having a faceplate 12 on the inner surface of which is a layer of phosphor 14, such as a mixture of 52% by weight of zinc sulfide and 48% by weight of -cadmium sulde. On the exposed surface of the phosphor layer 14 is a relatively thin layer of aluminum 16. The phosphor may have a thickness of from 0.6 to l mil and the aluminum layer may have a thickness of .O04 mil.

Spaced from the aluminum layer 16 witlun the envelope lll, `is a storage grid 18. Grid 18, as more clearly shown in FIGS. 2 and 3, includes a metallic mesh 2l) which may be made of a metal such as nickel or aluminum. The mesh 3 20 is suitably xe-d to a support ring 19. On the surface of the mesh 20 remote from the faceplate 12 is an outer layer 22 of zinc sulde and an intermediate blocking layer 24 of cadmium sulde. Further particulars of the grid 18 will be described hereinafter.

Spaced from the grid 18 in a direction remote from the faceplate 12, is a collector grid 26 (FIG. 1), the function of which will be described in the following and more detailed description.

The envelope 11 also includes a neck portion 28 remote from .the faceplate 12. In the neck portion 28 are suitably mounted three electron guns 30, 32, and 34.

A conductive coating 35, for example graphite, is applied to the inner surface of the envelope 11 and its neck portion 28. This coating is connected to a supply of +50 volts, and serves to preserve a desired uniform potential within the envelope 11 in the area surrounding the space between the gun and the screen. This uniform potential contributes to desired collimation of the beams produced by guns 30, 32 and 34.

THE STORAGE FUNCTION (a) Positive writing-Electron guns 30 and 32 are associated with the storage function of the tube 10. Gun 30 is a positive Writing gun and serves to establish a desired positive charge pattern on the storage grid 18. Gun 32 is a reading gun that is adapted to produce a flood of electrons which penetrate the grid 18 in accordance with the charge pattern on the grid, and impinge upon the phosphor screen 14, for producing a continuing or persistent visual display thereon. The aluminum coating 16 is sufficiently thin to permit the flood electrons to penetrate it and to reach the screen 14.

The writing gun 30 includes a cathode 36, a control or signal grid 38, accelerating anodes 40, 42 and an electrostatic focus electrode 44. Exemplary voltages employed `in the operation of gun may be as follows. The cathode 36 may have 2000 volts impressed on it. A signal or control ygrid 38 of this gun is connected to a signal input circuit known in the art and impressed with a bias of about 2010 volts. On each of the accelerating anodes 40 and 42, +150 volts is impressed. A beam forming electrode 44 is connected to an adjustable voltage supply providing a vo-ltage in a range including +1300 volts and adjusted for best focus.

A scanning system is employed for scanning the beam produced by gun 30 across the storage Igrid 18. This scanning system includes plates 46, 4S connected to a suitable horizontal deflection voltage generator Si), for horizontally deflecting the beam from gun 30; and plates 52, 54 connected to a vertical deflection voltage generator 56 for vertically deflecting the beam.

The beam produced by gun 30 has sufcient intensity or velocity to dislodge electrons from the coating 22 of the grid 18 by secondary emission, to provide a persistent pattern of lpositively charged areas on the storage grid 18. This beam intensity is such as to lie between the first and second cross-overs of the secondary emission characteristic icurve of the material of storage grid layer 22.

The reading or flood gun 32 includes a cathode 58 that may be operated at ground potential, a focusing electrode 62 connected to a -10 volt supply, and an accelerating electrode 63 operated at +150 volts. Some electrons in the beam from the flood gun 32 pass through the openings in the less negative areas of the grid 18 and impinge on the phosphor screen 14, while others are deected back by the more negative areas of the grid and are icollected by lcollector grid 26. It will be seen, therefore, that whether an electron is permitted to pass through the storage grid 18 or its deflected back, is dependent upon the electrical charge on the particular area of the target to which the electron is directed. Electrons passing through the grid 18 have suliicient kinetic energy to penetrate the thin aluminum layer 16 and to excite the phosphor screen 14 to luminescence.

Since the electrons from the flood gun 32 do not appreciably affect the charges on the storage grid 18 produced -by the beam of the writing gun 30, the display produced on the screen 14 is non-moving and may have a persistence of several minutes. This non-moving display is therefore adapted to serve advantageously as a background for a second and non-persistent display to be described.

(b) Negative writing-It is feasible according to the invention, to operate gun 34 in such a way as to cause it to charge the storage grid in a negative direction. This may be done by increasing the voltage on gun 34 to a more negative value than -6 kv., or by setting the mesh at a more negative voltage. With such altered voltage, conductivity through the dielectric zinc sulde would exceed secondary emission losses and would eventually bring the potential of the storage grid layer 22 to the potential of the mesh 20.

A representative negative voltage on the cathode of gun 34 for effecting negative writing, is +8 kv., with the mesh 20 kept at -8 volts. Alternatively, the cathode voltage may be retained at -6 kv. and the mesh voltage increased to -12 volts.

NON-STORAGE FUNCTIONS One non-storage function of tube 10 is performed by electron gun 34 in combination with the phosphor screen 14 and the storage grid 18. The gun 34 includes a cathode 64 connected to a -6 kv. supply. A control `grid 66 of this gun is connected to a signal input circuit known in the art and impressed with a bias of about 6020 volts. Accelerating anodes 68, 70 are each connected to a supply of volts. A beam focusing electrode 72 is connected to an adjustable voltage supply providing a voltage in a range including -4 kv., and adjusted for best focus. The beam produced by gun 34 is suitably deected horizontally by means of deection plates 74, 76 connected to horizontal deflection voltage generator 78. The beam is deflected vertically by plates 80, 82 connected to a vertical deflection voltage lgenerator 84.

The velocity of the beam produced by gun 34 with the power supplies indicated, is sufficiently high so that the electrostatic charges on the storage grid 18 have no appreciable elfect on this beam as it passes through the openings in the storage grid mesh. However, the relatively high velocity of the beam involves a voltage that is between the first and Second crossovers 0f the secondary emission characteristic curve of the material 22 of the storage grid 18, and therefore secondary emission ows from this material. To counteract this loss of electrons, the material of grid 18 is characterized by conductivity in response to electron bombardment, so that any electrons dislodged by secondary emission from material 22 of the grid 18, are compensated for by electrons provided as a consequence of the conductivity of the materials 22, 24 of the target electrode, when bombarded by electrons from gun 34.

In order that there be an exact correspondence between the number of electrons dislodged from the storage grid 18 by the beam from gun 34 and the electrons supplied to the storage grid by bombardment-induced conductivity, it is necessary that the voltage on the cathode 64 of gun 34- and the voltage impressed on the metal mesh 20 of the storage grid be critically related. In the instant example such correspondence is found to exist when the cathode 64 is operated at -6 kv. and the metal screen 20 (FIG. 2) of the storage grid 18 is energized by a supply of -8 volts.

This is illustrated by the graph shown in FIG. 4. In this graph, curve 86 is illustrative of the writing speed obtained by secondary emisson 'with zinc sull-ide operating between the rst and second crossovers of the secondary emission `characteristic of this material. Since the net loss of electrons by storage grid 18 renders it more positive, the curve 86 is illustrated as being positive in terms` of Writing speed. Curve 38 illustrates writing speed obtained by the bombardment-induced conductivity characteristic of the two target layers 22, 24, for electron iiow is a direction from the conductive mesh 20 to the outer layer 22. Since electrons supplied by such conductivity of the layers 22, 24 makes the storage grid 1S, in particular the outer surface of layer 22 of zinc sulfide, more negative, curve 88 is shown as a negative curve in terms of writing speed. The abscissa of the graph of FIG. 4 denotes the voltage on cathode 64 of gun 34 (FIG. l) and the ordinate is in terms of writing speed. Writing speed is measured in inch-volts per second, and can be either positive or negative. With positive writing, a written spot is brighter than before writing, while in negative writing, the written spot is darker than it was before writing.

It will be noted in the graph of Fi G. 4 that with a voltage of -6000 volts on the cathode 64 of gun 34, the writing speed due to secondary emission, as indicated by curve 86, has a certain positive magnitude. At this cathode voltage the writing speed due to bombardmentinduced conductivity as indicated by curve 88 which represents a voltage of -8 volts on the mesh, has the aforementioned certain magnitude but in a negative direction. This means that at the voltages indicated, the loss of electrons from the layer 22 of grid 1S by secondary emission, is continuously and exactly compensated for by the conduction of electrons to this layer from the metal mesh 20.

It will be seen, therefore, that under the conditions described above, the relatively high velocity or energy of the beam from gun 34 does not affect the charges previously laid down on the grid 18 by the lower energy beam produced by the writing gun 30. Furthermore, this velocity of the beam is appreciably greater than the velocity of the fiood beam produced by storage reading gun 32. This difference in beam velocity together with a possible difference in current densities of the two beams produce difierent effects on the phosphor screen 14, so that the nonstored display is distinguishable readily from the stored display.

THE STORAGE GRID The storage grid 18, shown best in FIGS. 2 and 3, comprises a structure including a metal mesh 20 supported `on a metal ring 19 (FIG. 1). One side (the side facing the guns) of the mesh 20 has thereon a first layer 24 of cadmium sulfide and a second or top layer 22 of zinc sulfide.

The metal mesh 20 may be made of a metal such as nickel or aluminum. It is preferably about 55 percent transparent with 250 openings per linear inch. The thickness of the mesh 20 may be from 1/2 to 11/2 mils. In the instant example the mesh 20 has a thickness of l mil. In the example under consideration, the mesh openings are square, Iwith corners slightly rounded.

The electroformed mesh 20 is fixed to the supporting ring 19 by welding or brazing. The supporting ring 19 may be made of nickel, sta-inless steel or any other metal having a coefficient of expansion slightly less than that of the mesh 20, and the required strength for supporting the mesh.

The resultant mesh-ring structure is baked in air for about one-half hour at a temperature of about 450 C. Applicant has found that baking in air is just as effective as baking in a reducing or inert atmosphere. The baking step serves to drive out gasses occluded in the material of the mesh and ring.

The baked mesh-ring structure, a boat containing cadmium sulfide, and a monitoring plate are then placed in a chamber adapted to be evacuated. The boat, monitoring plate, and chamber may be types known in the art and are therefore not shown in the drawing. In the instant example the boat, made of platinum or tantalum, is V-shaped and has a length of 2 inches and a width of 1/2 inch and contains a desired amount of cadmium sulfide. The monitoring plate is positioned to receive cadmium sulfide at the same rate as the evaporated coating is applied to the mesh, and to indicate the thickness of the coating received by the conventional light interference method.

After the monitoring plate and boat containing cadmium sulfide have been placed in the chamber, the chamber is evacuated to a pressure of about l06 millimeters of mercury for application of the layer 24 `of cadmium sulfide by evaporation from the boat to that face of the mesh 20 which will face the electron guns in the finished tube. This degree of vacuum (106 millimeters of mercury) is desirable in the interests of a satisfactory rate of evaporation desirably at a rate to increase the coating thickness by 25 Angstroms per minute. Lower rates are tolerable but they are objectionable in that they require a longer time for building up of the layer 24. The highest practical rate involves an increase in coating thickness of Angstroms per minute.

After evacuation of the chamber, the boat containing the cadmium sulfide is heated to a temperature to produce cadmium sulfide vapor at the desired rate, for example, to increase the coating thickness 25 Angstroms per minute. This temperature may be realized by heating the boat electrically by resistance losses therein. The temperature at which the boat is heated for evaporating the cadmium sulfide at the desired rate indicated is from 450 to 550 C. The mesh and ring structure is not deliberately heated during the foregoing evaporating operation.

After the cadmium sulfide has been applied to mesh 20 to a thickness of a value from 300 to 1500 Angstroms, determined by the monitoring plate, the boat is permitted to cool down naturally for about 10 minutes. The chamber in which the evaporation of the cadmium sulfide took place, is then filled with an inert gas such as nitrogen supplied from a tank under pressure. Thereafter the coated mesh is removed from the chamber and kept in a dry place, such as in a desiccator, until the next step of applying the zinc sulfide layer over the cadmium sulfide layer, is performed.

In applying the zinc sulfide layer 22, a second boat similar to the rst named boat and also made of platinum or tantalum and having the required amount of zinc sulfide therein, is placed in the chamber. Also placed in the chamber is a new monitoring plate and the mesh previously coated with cadmium sulfide. The chamber is evacuated to a pressure of about l0-6 millimeters of mercury. At this pressure the Zinc sulfide is evaporated at a rate of coating thickness increase of about 100 Angstroms per minute. Applicant has found that this is the best rate for depositing zinc sulfide. However, a practical rate range for zinc sulfide evaporation is from about 100 Angstroms per minute to 200 Angstroms per minute.

To realize the aforementioned best rate of increase in coating thickness of zinc sulfide, the boat is heated electrically to a temperature of 600 to 700 C. When the monitoring plate indicates a coating thickness of from 2000 to 6000 Angstroms, further heating of the boat is stopped and it is permitted to cool down for from l5 minutes to 1/2 hour. The chamber is then filled with nitrogen and the coated mesh is removed, and pending utilization in a storage tube, the mesh is kept temporarily in a desiccator.

During the temporary storage in the desiccator of the mesh 20 after each of the two applications thereto of the cadmium sulfide and Zinc sulfide, no special precautions are needed with respect to normal room light and temperature. No waiting at all is needed before utilization of the coated mesh in a storage tube. The lack of need for special precautions and for waiting are often advantageous in expediting the manufacture of a display storage tube.

To insure the thickness uniformity of the two layers of cadmium sulfide and zinc sulfide during the two evaporating operations described, when several meshes are coated simultaneously, the several meshes are disposed within the chamber in an array simulating a portion of the surface of a sphere. A boat containing the coating material and positioned at the focal point of this array, evaporates a coating or layer on each mesh that is uniform in thickness.

Cadmium sulfide possesses a characteristic that is advantageous in its use as described herein. While cadmium sulfide has a lower resistivity as a bulk material than zinc sulfide, applicant has found that when cadmium sulfide is disposed between nickel or aluminum and zinc sulde, there is formed an interface between the metal mesh and the cadmium sulfide. This interface has a blocking or rectifying characteristic. Thus, in the absence of electron bombardment of the storage layers, this interface prevents a fiow of electrons from the metal mesh to the storage layers when the potential difference between the mesh and the storage layers is in the direction in which such fiow would normally occur. However, when the storage layers are bombarded with electrons, the blocking or rectifying characteristic is nullified so that electrons are free to flow from the metal mesh to the storage layers.

It is not desirable to use cadmium sulfide alone as the dielectric storage layer on the metal mesh 20. This is for the reason that cadmium sulfide is characterized by appreciably low resistivity, and by bombardment-induced conductivity that is sustained for a short while after the bombardment terminates. These characteristics of cad mium sulfide would defeat the desired balance of the secondary emission and bombardment-induced conductivity. Harmful effects from the aforementioned low resistivity and persistence of bombardment-induced conductivity of cadmium sulfide are avoided when cadmium sulfide is employed in combination with zinc sulfide as described before herein.

What is claimed is:

1. A storage tube comprising (a) a storage grid including (1) a metal base,

(2) a first coating of cadmium sulfide in direct contact with said base, and

(3) a second coating of Zinc sulfide over said cadmium sulfide coating.

2. A storage tube comprising (a) a storage grid including (l) ametal base, Y

(2) a rst coating of cadmium sulfide in direct contact with said base, and

(3) a second coating of zinc sulfide over said cadmium sulfide coating,

(4) said second coating being thicker than said first coating.

3. A storage tube comprising (a) a storage grid including (l) a base made of a metal selected from the group consisting of nickel and aluminum,

(2) a first coating of cadmium sulfide on said base and partly diffused into the crystal structure of the material of said base to provide an interface that is current-blocking from said cadmium sulfide to said base and,

(3) a second coating of zinc sulfide over said cadmium sulfide coating.

4. A multimode direct-view display storage tube comprising:

(a) an elongated envelope,

(b) an electron gun in one end portion of said envelope and,

(c) a storage grid in and extending across the other end portion of said envelope,

(1) said storage grid comprising a base made of a metal selected from the group consisting of nickel and aluminum and having openings extending therethrough,

(2) said base having on the side thereof facing said gun a dielectric material comprising a first layer of cadmium sulfide and a second layer of zinc sulfide,

(3) said cadmium sulfide forming With said metal an interface that exhibits a rectifying property in the direction from said base to said dielectric, said interface blocking current flow from said dielectric to said base.

5. A multimode direct-view storage tube comprising a storage grid including:

(a) a fiat apertured metal base, and

(b) a dielectric material covering one face of said base while leaving the apertures of the base substantially unobstructed,

(c) said dielectric material comprising a layer of cadmium sulfide in contact with said one face of said base and a layer of zinc sulfide over said layer of cadmium sulfide.

6. A multimode direct-view storage tube comprising a storage grid including:

(a) an apertured base made of a metal selected from the group consisting of nickel and aluminum, and

(b) a dielectric material covering one face of said base while leaving the apertures in the base substantially unobstructed,

(c) said dielectric material including a layer of cadmium sulfide in Contact with said one face of said base, and a layer of zinc sulfide over said layer of cadmium sulfide.

7. A multimode direct-view storage tube comprising a storage grid including:

(a) a flat apertured metal base made of a metal selected from the group consisting of nickel and aluminum, and

(b) a dielectric material covering one face of said base while leaving the apertures in the -base substantially unobstructed,

(c) said dielectric material including a layer of cadmium sulfide in contact with said one face of said base and a layer of zinc sulfide over said layer of cadmium sulfide, a portion of said layer of cadmium sulfide forming an interface with a portion of the metal of said base, said interface permitting current fiow, only from said base to said dielectric material, whereby a stored positive charge on said material is restrained from migration to said base.

8. A multimode direct-view storage tube comprising a storage grid including:

(a) a fiat apertured metal base, and

(b) a dielectric material covering one face of said base while leaving the apertures in the base substantially unobstructed,

(c) said dielectric material consisting of an outer layer of zinc sulfide and a layer of cadmium sulfide intermediate said outer layer and said base,

(d) said layer of cadmium sulfide having a thickness of from 300 to 1500 Angstroms.

9. A multimode direct-view storage tube comprising a storage grid including:

(a) a fiat apertured base made of a metal selected from the group consisting of nickel and aluminum, and

(b) a dielectric material covering one face of said base while leaving the apertures in the base substantially unobstructed,

(c) said dielectric material consisting of a layer of cadmium Sulde in contact with said base and an outer layer of Zinc sulfide,

(d) said outer layer of zinc sulfide having a thickness of from 2000 to 6000 Angstroms.

10. A direct-view display storage tube comprising:

(a) a screen adapted to luminesce in response to electron impingement thereon,

(b) a storage grid spaced from said screen,

(c) means for charging said grid by secondary electron emission to provide a predetermined stored electrostatic charge pattern thereon,

(d) means for providing a persistent visible display on said screen conforming to said charge pattern,

(e) said grid comprising a conductive mesh having thereon a storage body comprising a first layer of cadmium sulfide and a second layer of zinc sulfide,

(l) said storage body having secondary emission and bombardment-induced conductivity characteristics whereby loss of electrons from said storage body by secondary emission is compensated for by electrons supplied by the bombardment-induced conductivity of said storage body in response to a beam of electrons having a predetermined energy level above the energy level of said persistent display-producing means,

(f) means for producing a beam of electrons having said predetermined energy level,

(g) means for scanning said beam of electrons across said storage body and across the openings in said mesh, whereby the portion of said beam passing through said openings impinges on said screen to provide thereon a visible display that is dif-ferent from said persistent visible display, and the previously formed charge pattern on said storage body is preserved.

11. A multimode direct-view display storage tube cornprising:

(a) a screen adapted to luminesce in response to electron impingement thereon,

(b) a storage grid spaced from said screen,

(c) means for charging said grid by secondary electron emission to provide la predetermined stored electrostatic charge pattern thereon,

(c) means for charging said grid by secondary electron emission to provide a predetermined stored electrostatic charge pattern thereon,

(d) means for providing a persistent visible display on said screen conforming to said charge pattern, said grid comprising an apertured conductive mesh having thereon a storage body comprising a first layer of cadmium sulfide and a second layer of zinc sulde, said storage body leaving the apertures in said mesh substantially unobstructed,

(1) said storage body having secondary emission and bombardment-induced conductivity characteristics whereby loss of electrons from said storage body by secondary emission is compensated for by electrons supplied by the bombardment-induced conductivity of said storage body in response to a beam of electrons having a predetermined energy level above the energy level of said persistent display-producing means,

(e) means for producing a beam of electrons having said predetermined energy level, and

(f) means for scanning said beam of electrons across said storage body and the openings in said mesh, whereby said beam impinges on said screen to provide thereon a visible display that is different from said persistent visible display, and the previously formed charge pattern on said storage body is preserved.

12. A direct-view display storage tube comprising:

(a) a phosphor screen adapted to luminesce in response to electron impingement thereon,

(b) a storage grid closely closed from said screen,

(c) means spaced from the side of said grid remote from said screen, for 'charging said grid by secondary electron emission to provide a predetermined stored electrostatic charge pattern thereon,

(d) means for providing a persistent visible display on said screen conforming to said charge pattern,

(e) said grid comprising a at apertured conductive mesh having on said side thereof a storage body comprising dielectric material including a layer of cadmium sulfide in contact with said mesh and a layer of zinc sulde over said layer of cadmium sulfide,

(l) said storage dielectric material having secondary emission and bombardment-induced conductivity characteristics whereby loss of electrons from said storage body by secondary emission is compensated for by electrons supplied by the bombardment-induced conductivity of said storage body in response to a beam of electrons having a predetermined energy level above the energy level of said persistent display-producing means,

(f) means for producing a beam of electrons having said predetermined energy level, and

(g) means for scanning said beam of electrons across said storage body and across the openings in said mesh, whereby said beam impinges on said screen to provide thereon a visible display that is different from said persistent visible display and the previously formed charge pattern on said storage body is preserved.

References Cited bythe Examiner UNITED STATES PATENTS 7/l953 Williams 313-65 X 4/1959 Smith 315-13 X 

10. A DIRECT-VIEW DISPLAY STORAGE TUBE COMPRISING: (A) A SCREEN ADAPTED TO LUMINESCE IN RESPONSE TO ELECTRON IMPINGEMENT THEREON, (B) A STORAGE GRID SPACED FROM SAID SCREEN, (C) MEANS FOR CHARGING SAID GRID BY SECONDARY ELECTRON EMISSION TO PROVIDE A PREDETERMINED STORED ELECTROSTATIC CHARGE PATTERN THEREON, (D) MEANS FOR PROVIDING A PERSISTENT VISIBLE DISPLAY ON SAID SCREEN CONFORMING TO SAID CHARGE PATTERN, (E) SAID GRID COMPRISING A CONDUCTIVE MESH HAVING THEREON A STORAGE BODY COMPRISING A FIRST LAYER OF CADMINUM SULFIDE AND A SECOND LAYER OF ZINC SULFIDE, (1) SAID STORAGE BODY HAVING SECONDARY EMISSION AND BOMBARDMENT-INDUCED CONDUCTIVITY CHARACTERISTICS WHEREBY LOSS OF ELECTRONS FROM SAID STORAGE BODY BY SECONDARY EMISSION IS COMPENSATED FOR BY ELECTRONS SUPPLIED BY THE BOMBARDMENT-INDUCED CONDUCTIVITY OF SAID STORAGE BODY IN RESPONSE TO A BEAM OF ELECTRONS HAVING A PREDETERMINED ENERGY LEVEL ABOVE THE ENERGY LEVEL OF SAID PERSISTENT DISPLAY-PRODUCING MEANS, (F) MEANS FOR PRODUCING A B EAM OF ELECTRONS HAVING SAID PREDETERMINED ENERGY LEVEL, (G) MEANS FOR SCANNING SAID BEAM OF ELECTRONS ACROSS SAID STORAGE BODY AND ACROSS THE OPENINGS IN SAID MESH, WHEREBY THE PORTION OF SAID BEAM PASSING THROUGH SAID OPENINGS IMPINGES ON SAID SCREEN TO PROVIDE THEREON A VISIBLE DISPLAY THAT IS DIFFERENT FROM SAID PERSISTENT VISIBLE DISPLAY, AND THE PREVIOUSLY FORMED CHARGE PATTERN ON SAID STORAGE BODY IS PRESERVED. 